The photophysics and charge state dynamics of the nitrogen vacancy (NV) center in diamond has been extensively investigated, but is still not fully understood. In contrast to previous work, we find that
NV0 converts to ${\mathrm{NV}}^{\ensuremath{-}}$ under excitation with low power near-infrared (1064-nm) light, resulting in increased photoluminescence from the ${\mathrm{NV}}^{\ensuremath{-}}$ state. We used a combination of spectral and time-resolved photoluminescence experiments and rate-equation modeling to conclude that
NV0 converts to ${\mathrm{NV}}^{\ensuremath{-}}$ via absorption of 1064-nm photons from the valence band of diamond. We report fast quenching and recovery of the photoluminescence from both charge states of the NV center under low power 1064-nm laser excitation, which has not been previously observed. We also find, using optically detected magnetic resonance experiments, that the charge transfer process mediated by the 1064-nm laser is spin dependent.
The spin dynamics of the negatively charged nitrogen-vacancy (NV⁻) centers in diamond are highly sensitive to quantum electromagnetic fluctuations arising from optical excitation, chemical interactions, and thermal processes. Here we investigated the optical and spin properties of ensembles of NV⁻ centers in diamond under continuous-wave (CW) and nanosecond pulsed laser excitation. Optical detection of magnetic resonance (ODMR) is employed to monitor laser induced shifts of the zero-field splitting parameter D under ambient and high-vacuum conditions. Increasing CW laser power results in a systematic downshift of the resonance frequency due to laser-induced heating. The effect is significantly enhanced under vacuum, where the shift in D reaches up to ~17 MHz, compared to ~5 MHz in air, emphasizing the role of environmental thermal dissipation. Under nanosecond pulsed excitation, increasing the pulse repetition rate similarly leads to resonance shifts and reduced ODMR contrast, consistent with cumulative thermal effects. Visible and infrared spectroscopy confirm power dependent modifications of NV emission. Time resolved photoluminescence measurements showed that the excited-state lifetime (~6 ns) remains nearly constant across the investigated excitation range, indicating that in this regime the dominant limitation is thermal loading of the spin resonance rather than a change in intrinsic radiative decay dynamics. These results provide a comprehensive characterization of thermal effects in high power optical excitation of NV ensembles and are directly relevant for high intensity NV-based sensing and spectroscopy, particularly in vacuum environments.
We report on time-resolved photoluminescence of a free-exciton in IIa chemical vapor deposition diamond crystal. Large difference between decay times for one- and two-photon excitation processes was observed. The longest room-temperature exciton photoluminescence lifetime τ(FE)=220 ns was obtained under two-photon excitation with a photon energy of 4.7 eV. The role of diffusion and surface recombination velocity in exciton photoluminescence dynamics was studied using a new optical method based on two-photon excited time-resolved photoluminescence. The measured room-temperature value of diffusion coefficient in diamond was D=40 cm(2)/s.